Views: 2 Author: Xicheng Ep Ltd Publish Time: 2022-02-25 Origin: Xicheng Ep Ltd
1. Overview of Asphalt Flue Gas
In the production process of various asphalt-based waterproof materials, asphalt needs to be heated, transported, and made into asphalt-based mixtures that meet various process requirements for production use. During this process, a large amount of bitumen flue gas will be generated. The flue gas contains a variety of organic substances, including carbocyclic hydrocarbons, cyclic hydrocarbon derivatives and other compounds, many of which are harmful to human health. Asphalt smoke contains various polycyclic aromatic hydrocarbons such as benzopyrene, benzanthracene, and carbazole. Most of them are carcinogenic and strong carcinogens. The particle size is mostly between 0.1 and 1.0 μm, the smallest is only 0.01 μm, and the largest is about 10.0 μm, especially a variety of carcinogens represented by 3,4-benzene. substance. The main way that asphalt fumes endanger human health is to adhere to the floating dust below 8 um and be inhaled into the human body through the respiratory tract. Asphalt flue gas mainly exists in the form of tar fine mist particles of 0.1-1.0um. Its purification treatment is to capture these tiny particles as much as possible, so that the emission of flue gas can meet relevant standards without causing secondary pollution. Therefore, it is very necessary to purify and treat asphalt flue gas so that the emission can meet atmospheric environmental standards.
2. Asphalt flue gas treatment method
According to the main components of asphalt flue gas are carbocyclic hydrocarbons, cyclic hydrocarbon derivatives, organic waste gas, dust particles, and tar-containing pollutants, the current treatment methods for asphalt flue gas include spray + electrostatic + activated carbon adsorption, spray + electrostatic + ion purification method, spraying + static electricity + combustion method, spraying + static electricity + UV photolysis method, etc., introduce the asphalt flue gas treatment method in detail.
2.1 Wet washing method
Asphalt fumes are dusty, hot, and contain tar. The main purpose of the wet scrubber is to cool down and remove dust. The bitumen flue gas is collected by the pipeline and enters the scrubbing tower, the water enters from the top of the scrubbing tower, and flows down step by step along the inner rotating plate of the tower. Full contact absorption and heat transfer are carried out on the upper part of the system. After cooling and dust removal, the exhaust gas enters the electrostatic equipment to remove the tar-containing flue gas.
2.2 Electrostatic ionization method
After being cooled by the spray tower and dedusted, the asphalt flue gas enters the electrostatic equipment. The electrostatic equipment uses the electrostatic force generated by the high-voltage electric field to separate the tar in the flue gas, and separates the tar from the asphalt flue gas under the action of the electric field. gas.
2.3 Organic waste gas treatment methods
Organic waste gas treatment methods mainly include activated carbon adsorption method, ion purification method, combustion method, UV photolysis method, etc. Detailed explanation:
(1) Activated carbon adsorption method
The main principle of adsorption method is to use porous solid adsorbent (activated carbon, silica gel, molecular sieve, etc.) to treat organic waste gas, so that harmful components can be fully adsorbed through chemical bond force or molecular attraction, and then adsorbed on the surface of the adsorbent, thereby To achieve the purpose of purifying organic waste gas. The adsorption method is currently mainly used in the purification of low-concentration organic waste gas with large air volume, low concentration (≤800mg/m3), no particulate matter, no sticky matter, and normal temperature.
Activated carbon has a high purification rate (activated carbon adsorption can reach more than 90%), is widely used, simple to operate, and low investment. After the adsorption is saturated, it is necessary to replace the new activated carbon, and the replacement of the activated carbon requires a cost. The replaced activated carbon after saturation also needs to be treated by professionals for hazardous waste treatment, and the operating cost is high.
(2) Ion purification method
The plasma method utilizes the characteristics of extremely high chemical activity generated inside the plasma, uses a high-voltage discharge device to generate high-energy electrons and ions during discharge, separates oxygen molecules in the air, and generates free oxygen ions after the oxygen molecules absorb energy. The waste gas pollutants react with free oxygen groups and are finally converted into substances such as CO2 and H2O, so as to achieve the purpose of purifying the waste gas.
This method has the characteristics of wide application range, high purification efficiency, and small equipment footprint, and is suitable for organic gases that are difficult to handle by other methods; The space is prone to explosions and there are potential safety hazards, thus limiting its use.
(3) Combustion method
The combustion method only burns volatile organic compounds completely under the conditions of high temperature and sufficient air, and decomposes them into CO2 and H2O. Combustion method is suitable for all kinds of organic waste gas, which can be divided into direct combustion, thermal combustion and catalytic combustion.
The high-concentration waste gas with waste gas concentration greater than 5000mg/m³ generally adopts the direct combustion method. This method uses organic waste gas as fuel for combustion. The combustion temperature is generally controlled at 1100 ℃, and the treatment efficiency is high, which can reach 99%.
The thermal combustion method is suitable for the treatment of waste gas with a concentration of 1000-5000 mg/m³. The thermal combustion method has a low concentration of organic waste gas and needs to use other fuels or combustion-supporting gases. The temperature required for thermal combustion is lower than that of direct combustion, about 540 -820℃. Combustion treatment of organic waste gas has high treatment efficiency, but if the organic waste gas contains elements such as S and N, the waste gas generated after combustion is directly discharged out, which will lead to secondary pollution.
The purification rate of organic waste gas is relatively high by thermal combustion or catalytic combustion, but its investment and operation cost is extremely high. Due to the many and scattered points of exhaust emission, it is difficult to achieve centralized collection. Combustion devices require multiple sets and require a large footprint. Thermal combustion is more suitable for 24-hour continuous operation and high concentration and stable exhaust gas conditions, not suitable for intermittent production line conditions. The investment and operating costs of catalytic combustion are lower than those of thermal combustion, but the purification efficiency is also relatively low; however, precious metal catalysts are easily poisoned and fail due to impurities in the exhaust gas (such as sulfides), and the cost of replacing the catalyst is high; at the same time The control of exhaust gas intake conditions is very strict, otherwise the catalytic combustion chamber will be blocked and safety accidents will be caused.
(4) UV photolysis method
The UV photolysis purification method uses high-energy UV ultraviolet beams to decompose oxygen molecules in the air to generate free oxygen (that is, reactive oxygen species). Since the positive and negative electrons carried by free oxygen are unbalanced, they need to combine with oxygen molecules to generate ozone. Ozone has a strong The organic waste gas and malodorous gas are degraded and converted into low-molecular-weight compounds, CO2 and H2O through the synergistic photolysis and oxidation of organic waste gas and malodorous gas by ozone.
UV photolysis has high treatment efficiency, which can reach more than 95%; strong adaptability, can adapt to the purification treatment of medium and low concentration, atmospheric volume, different organic waste gas and malodorous gas substances; product performance is stable, stable and reliable operation, 24 hours a day Continuous work; low operating cost, low equipment energy consumption, no need for special management and maintenance, only regular inspections. The UV photolysis method adopts the principle of photolysis, and the module adopts explosion-proof treatment, which eliminates potential safety hazards, has high fireproof, explosion-proof and anti-corrosion performance, and has safe and stable equipment performance. It is especially suitable for industries with high explosion-proof requirements such as chemical industry and pharmacy.
The above introduction to the asphalt flue gas treatment method, I hope it can help you. In fact, for the asphalt flue gas treatment, it is generally necessary to design according to the concentration of the exhaust gas, the amount of production, the composition of the exhaust gas, and how to collect it.